[I have original ReSource 4.x, 5.x and 6.01, 6.06 packages.] From memory, ReSource version 6 came with the same manual as version 5, which was not hugely different from versions 3 & 4. I don't think anyone has scanned the ReSource version 5 manual, but that might be worthwhile to do.
....

Zipped PDF of the Manual for V5/V6 is in the zone now.

Rather large, but nice and clear to read, especially the code examples.

Knock yourselves out!

Incidentally, IDA is very nice for a "one-size-fits-all" dissassembler, but ReSource V6.06 is definitely the go for serious Amiga work.

V6.06 still has several bugs, but nothing too drastic, these 2 immediately spring to mind:

1. Creates .w offsets for some .b type branches when near the +/-127/128 byte offset limits. Especially when branching ahead.

2. Creates incorrect word offsets when code with an offset in the relocation table resolves to an absolute location outside the HUNK that the relocation table belongs to.
(The apple2000 V1.3 emulator is a good example of this).
In reality, this is pretty hacky hand-assembly anyway. Doubt you would ever see a compiler produce such code.